Field of the Disclosure
Embodiments of the present application relates to the art of a drive control system for a hybrid vehicle having an engine, two motors and a power distribution device, in which an operating mode is switched by manipulating clutches to change a power transmission route.
Discussion of the Related Art
JP-A-2012-071699 describes one example of a hybrid vehicle comprising: a power distribution device having an input element connected to an engine, a reaction element connected to a first motor, and an output element connected to drive wheels; and a second motor applying a torque to an output side of the power distribution device. JP-A-2011-063136 also describes a hybrid vehicle of this kind. According to the teachings of JP-A-2012-071699 and JP-A-2011-063136, an operating mode of the hybrid vehicle can be selected from: a series parallel mode, in which power generated by an engine is partially converted into an electric power by the first motor while delivering the remaining power to drive wheels, and a the motor is driven by the electric power generated by the first motor to generate driving force; a series mode in which an output power of the engine is converted into an electric power by the first motor to drive the second motor by the generated electric power; and an electric vehicle mode in which the vehicle is powered by the second motor while stopping the engine. The operating mode is switched by manipulating a plurality of clutches.
The hybrid vehicle taught by JP-A-2012-071699 is provided with a first clutch that selectively provide a connection between the engine and the power distribution device, and a second clutch that selectively provide a connection between the engine and the first motor. According to the teachings of JP-A-2012-071699, specifically, the series parallel mode is established by engaging the first clutch while disengaging the second clutch, and the electric vehicle mode is established by disengaging the first clutch while engaging the second clutch. A control system taught by JP-A-2012-071699 is configured to stop the engine promptly when shifting from the series parallel mode to the electric vehicle mode by delivering output torque of the first motor to the engine while engaging the second clutch to connect the engine to the first motor
In the electric vehicle mode, it is preferable to further select the operating mode from a mode in which the first motor is rotated passively and a mode in which a rotation of the first motor is halted depending on a state of charge of a battery. However, in the hybrid vehicles taught by JP-A-2012-071699 and JP-A-2011-063136, the operating mode cannot be further selected in the electric vehicle mode.
In order to establish the above-mentioned modes of the electric vehicle mode, it is necessary to manipulate a plurality of clutches (including a brake) to alter the power transmission route. However, if only a specific clutch is engaged to switch the operating mode from the mode in which the vehicle is powered by the engine to the electric vehicle mode, a complicated control is required and an engagement shock of the clutch may be caused. Specifically, the above-mentioned modes of the electric vehicle mode are selected on the basis of a required driving force, a vehicle speed, a state of charge of the battery etc. To this end, a specific control to select the operating mode of the EV mode is required, and the clutches have to be engaged and disengaged consecutively to shift the operating mode without delay.